When I open the door of my appliance, smoke rolls out, why?

Many appliance and chimney problems can be traced to excessive cooling of the chimney inner liner. Some common indications of cold liners include, excessive creosote and water vapour condensation, slow build-up of draft when a fire is started, smoke roll-out when the loading door is opened and greater likelihood of flow reversal or back drafting.

Many contributors to smoke roll-out is traced to the chimney being too large for the appliance. Another is most likely negative pressure throughout the house.